New CH pipework

[an203888]

Hi all. I have a 1970s house with a Ideal Mexico boiler on a vented system with a single heating zone. I am adding a single storey 40m2 extension and am just thinking about heating.

As im adding the new extension, this seems a good time to disregard the downstairs copper pipe in the floor (rather than wait for it to leak) and replace with a new run of 22mm speedfit to then branch off to rads. I will then create a second zone for this so I can control upstairs and downstairs seperatly.

My question is really about running the pipe. I am vaugely aware that pipe isnt supposed to be run in screed anymore, or it can but needs to be in some conduit. Is this correct? So the channels I dig for the pipe wold be quite hefty?
Alternativly the extension will be using a beam and block floor so could the 22 pipe be run under that in the void with some Armaflex around it?
How far can the 15mm take-offs be run from the 22mm pipe, could I run one up to 5 meters to a 2.5kw rad?
Lastly is it possible to run 10mm microbore pipe for the last section as it comes out of the floor/wall. I think this looks neater than having 15mm pipes.

Thanks for your help in advance

 

[John D v2.0]

If you put any fittings in screed you have to make sure ample space for expansion and contraction. I think speedfit do special boxes for in screed pipework and fittings.
Personally I'd try to keep ch pipe work on the warm side of any insulation as much as possible, although the thick pipe insulation is good it's warm all the time so it's a constant heat loss.

 

[an203888]

If you put any fittings in screed you have to make sure ample space for expansion and contraction. I think speedfit do special boxes for in screed pipework and fittings.
Personally I'd try to keep ch pipe work on the warm side of any insulation as much as possible, although the thick pipe insulation is good it's warm all the time so it's a constant heat loss.

I've had a good look and although I can find Speedfit conduit, I can't find boxes. Come on guys, how is this usually done?

 

[oldbutnotdead]

If the copper was done properly it'll see you out
Have you done heat loss sums for your new extension, does the boiler have enough spare capacity to heat the extra space?
Don't bury plastic pipe couplers anywhere inaccessible, they are not maintenance free and will need attention at some stage.

If you want true multiple zones you'll have to tee off somewhere near the boiler, be aware that there may be a requirement for a bypass radiator (depends on your current setup, if it is proper old school gravity hot water pumped heating then less of an issue as long as you don't zone off the hot water as well). Also you are not allowed plastic within a metre of the boiler.

You can't select pipe size by what looks pretty, it is all about how much energy that pipe can carry at a sensible water speed (1m/s is max desirable). Google the figures, be aware that internal diameter of plastic tube will be at least 2mm less than the same external diameter copper tube. Then design your pipework so only plastic pipe is buried in ducting, fittings remain accessible.

 

[denso13]

how is this usually done?

For example https://www.bes.co.uk/3-m-underfloor-pipe-duct-16538

 

[an203888]

If the copper was done properly it'll see you out
Have you done heat loss sums for your new extension, does the boiler have enough spare capacity to heat the extra space?
Don't bury plastic pipe couplers anywhere inaccessible, they are not maintenance free and will need attention at some stage.

If you want true multiple zones you'll have to tee off somewhere near the boiler, be aware that there may be a requirement for a bypass radiator (depends on your current setup, if it is proper old school gravity hot water pumped heating then less of an issue as long as you don't zone off the hot water as well). Also you are not allowed plastic within a metre of the boiler.

You can't select pipe size by what looks pretty, it is all about how much energy that pipe can carry at a sensible water speed (1m/s is max desirable). Google the figures, be aware that internal diameter of plastic tube will be at least 2mm less than the same external diameter copper tube. Then design your pipework so only plastic pipe is buried in ducting, fittings remain accessible.

Thanks for this reply I will take it all on board. However the main issue I can see is where people talk about keeping plastic push fit fittings accessible.... When teeing off the main run to go to a rad (when pope is in floor), how is this even possible?

 

[oldbutnotdead]

Thanks for this reply I will take it all on board. However the main issue I can see is where people talk about keeping plastic push fit fittings accessible.... When teeing off the main run to go to a rad (when pope is in floor), how is this even possible?

You tee off where the pipe isn't under the floor of course. That's part of the design job....or if you have no choice then you form some sort of permanent access point so that you can get at the joint later on (it is acceptable to have a floor trap under carpet. If you do something like that then document exactly where the floor or wall traps are- pics, measurements, whatever- and store the documents near the boiler for your or someone else's future reference.)
Plastic installations work best using a manifold setup- large bore runs to an accessible central point then one piece feeds and returns to each radiator (no joints, elbows or Ts) rather than the traditional (copper) method of trunk and drop. May not be the best for thermal efficiency but definitely quicker and easier to install and cheaper (plastic pipe is cheaper than copper pipe, plastic fittings are more expensive than copper fittings)

 

[an203888]

You tee off where the pipe isn't under the floor of course. That's part of the design job....or if you have no choice then you form some sort of permanent access point so that you can get at the joint later on (it is acceptable to have a floor trap under carpet. If you do something like that then document exactly where the floor or wall traps are- pics, measurements, whatever- and store the documents near the boiler for your or someone else's future reference.)
Plastic installations work best using a manifold setup- large bore runs to an accessible central point then one piece feeds and returns to each radiator (no joints, elbows or Ts) rather than the traditional (copper) method of trunk and drop. May not be the best for thermal efficiency but definitely quicker and easier to install and cheaper (plastic pipe is cheaper than copper pipe, plastic fittings are more expensive than copper fittings)

Yeh I can see why someone might use the manifold approach. However I can see where my pipe wouldn't be under the floor. If I plan to run 22mm pipe under all rads and then tee off.... The 22mm pipe would always be in the floor, it's not feasible to have it come above the floor just for connection.

Just to be clear here, I don't mind copper or soldering it but have seen some horrible issues with it leaking in concrete/screed Ed floors and want a better option.

 

[oldbutnotdead]

If you're having a screeded floor then use some of that ducting that someone linked to- its designed to be cast into the screed & then lidded with 12mm ply, looks quite neat. Under carpet it would work fine & provide access (inconvenient but not impossible), under laminate or engineered timber more of an issue. (You'd have to run it round the room perimeter and tee straight up to the rads- best to avoid crossovers, you've only got 50mm).
Or you could run the 22mm round the walls at low level and hide them with slightly thick skirting board (depends what the walls are made of & whether you're going plaster on blocks or dot and dab plasterboard & skim. If the latter there's 20mm of space for a pipe duct if you stop the boards say 100mm above FFL, you can hide insulated 22s if you use 163mm skirting and block it out with 20mm batten at the top where it fixes to the wall. There used to be some clipon plastic trim for pipes that looked like skirting- not my thing, I like timber but might work for you.
EDIT The above suggestions for copper and soldered joints. For placcie the couplers/tees are too big to hide as well as not being maintenance free so you'd duct as many F & R pairs of 15mm as you needed from an (accessible) manifold and drop them off to each radiator.

 

[Ian H]

Thanks for this reply I will take it all on board. However the main issue I can see is where people talk about keeping plastic push fit fittings accessible.... When teeing off the main run to go to a rad (when pope is in floor), how is this even possible?

I’ve got a couple of speedfit T’s that will be under my floor, i’m going to put them into a cube of Celotex which I could access if I ever need to.

 

[an203888]

After the cmments on here and talking to a plumber I will be creating a manifold for the downstairs and running 15 or 10mm pipe to each radiator so no joins in floor etc

 

[ScottishGasMan]

That sounds like the best bet, this is what I've done on my house (not screwed but very little under floor space and all laminate flooring over it)

If feesable go for copper microbore rather than plastic, plastic wont carry as much heat (flow rate) as copper and will block so much easyer.